The major objectives of this proposal are: (1) to develop a behavioral assay for screening large numbers of mutagenized mice in a high-throughput environment; and (2) following protocol development and validation, to begin acquiring reference data on standard inbred mouse strains. Our approach will be to develop a technique for estimating the threshold of stimulus-induced sniffing (i.e., respiratory changes) in response to odors, as a method for the rapid quantification of odorant sensitivity. We propose to combine elements of the rigorous psychophysical techniques that are standard in our laboratory with elements from simpler techniques used in olfactory behavioral research. Specifically, we will: (1) apply our experience in measuring an animal's sniffing behavior in response to the presentation of odorant stimuli; (2) apply taste-potentiated odor aversion conditioning to improve stimulus control over the reflexive or unconditioned sniffing response to the presentation of odorant, and thereby increase the sensitivity and reliability of the measure; (3) apply our experience with computer-controlled olfactometry to provide precise control over stimulus generation and delivery; and (4) apply our automated tracking paradigm to rapidly acquire, in a single brief testing session, a threshold estimate of stimulus-induced sniffing. Using our OMP knockout mice as a "gold standard" (i.e., an animal in which a specific gene defect results in an alteration in function without anosmia), we will directly test the efficacy of the procedure to identify a mutant phenotype. Moreover, applying epidemiologic screening principles to the distributions of thresholds for stimulus-induced sniffing in OMP-null and congenic controls, we will establish an operational procedure for the evaluation of unknown animals. We have divided the assay development into five phases designed to: (1) define an appropriate measure of sniffing behavior that is altered between air and odorant stimuli; (2) directly evaluate whether taste-potentiated odor aversion conditioning significantly increases the precision and lowers the threshold for stimulus-induced sniffing, as compared to non-aversion conditioned animals; (3) evaluate the sensitivity, specificity and predictive value of the screening procedure to identify OMP-null mutants, establish comparative reference data for OMP-null and congenic control animals and, on the basis of these data, establish an operational procedure for the future screening of unknown animals; (4) evaluate additional odorants for their utility in the screening procedure; and (5) initiate collection of reference data on inbred strains of mice. For each phase, we will provide detailed information via a Web-based database linked to centralized resources.